Thermal efficiency and engine-out emissions from an internal combustion engine are determined by many factors including the combustion system design and the mechanical design. Combustion system design includes combustion chamber shape, the fuel injection nozzle, and the fuel injection pressure, intake manifold and exhaust manifold, etc. All of these together are optimized to achieve mixing quality that leads to effective combustion. Much is known and much has been studied in typical diesel engine combustion systems to determine what chamber shape and fuel injection characteristics lead to the desired output. However, in unconventional engines, less is known about what combustion chamber shape and fuel injection characteristics can provide the desired mixing and engine performance.
Such an unconventional engine, an opposed-piston, opposed-cylinder (OPOC) engine 10, is shown isometrically in FIG. 1. An intake piston 12 and an exhaust piston 14 reciprocate within each of first and second cylinders (cylinders not shown to facilitate viewing pistons). An intake piston 12′ and an exhaust piston 14 couple to a journal (not visible) of crankshaft 20 via pushrods 16. An intake piston 12 and exhaust piston 14′ couple to two journals (not visible) of crankshaft 20 via pullrods 18, with each intake piston 12 having two pullrods 18. The engine in FIG. 1 has two combustion chambers formed between a piston top 22 of intake piston 12 (or 12′) and a piston top 24 of exhaust piston 14 (or 14′) and the cylinder wall (not shown). The pistons in both cylinders are shown are at an intermediate position in FIG. 1. Combustion is initiated when the pistons are proximate each other. The piston tops 22 and 24 in FIG. 1 may not be optimized to provide the desired performance.